Incoherently beam combined (IBC) lasers combine the output from an array of gain elements or emitters (typically consisting of semiconductor material, such as GaAlAs, InP, GaAs, InGaAs, InGaAsP, AlGaInAs, and/or the like, which is capable of lasing at particular wavelengths) into a single output beam that may be coupled into, for example, an optical fiber. The gain elements may be discrete devices or may be included on an integrated device. Due to the geometry of IBC lasers, each gain element tends to lase at a unique wavelength. Exemplary arrangements of IBC lasers are described in U.S. Pat. No. 6,052,394 and U.S. Pat. No. 6,192,062.
FIG. 1 depicts a prior art arrangement of components in IBC laser 10. IBC laser 10 includes emitters 12-1 through 12-N which are disposed in a substantially linear configuration that is perpendicular to the optical axis of collimator 15 (e.g., a lens). Collimator 15 causes the plurality of beams produced by emitters 12-1 through 12-N to be substantially collimated and spatially overlapped on a single spot on diffraction grating 16. Additionally, collimator 15 directs feedback from partially reflective component 17 via diffraction grating 16 to emitters 12-1 through 12-N.
Diffraction grating 16 is disposed from collimator 15 at a distance approximately equal to the focal length of collimator 15. Furthermore, diffraction grating 16 is oriented to cause the output beams from emitters 12-1 through 12-N to be diffracted on the first order toward partially reflective component 17. Partially reflective component 17 causes a portion of optical energy to be reflected. The reflected optical energy is redirected by diffraction grating 16 and collimator 15 to the respective emitters 12-1 through 12-N. Diffraction grating 16 angularly separates the reflected optical beams causing the same wavelengths generated by each emitter 12-1 through 12-N to return to each respective emitter 12-1 through 12-N thereby locking each emitter at a unique wavelength. The grating effectively multiplexes the light from the array of emitters 12-1 through 12-N. Also, diffraction grating 16 is operable to demultiplex the reflected beams from partially reflective component 17.
It shall be appreciated that the geometry of external cavity 13 of IBC laser 10 defines the resonant wavelengths of emitters 12-1 through 12-N. The center wavelength (λi) of the wavelengths fed back to the ith emitter 12-i is given by the following equation: λi=A[sin(αi)+sin(β)]. In this equation, A is the spacing between rulings on diffraction grating 16, αi is the angle of incidence of the light from the ith emitter on diffraction grating 16, and β is the output angle which is common to all emitters 12-1 through 12-N. As examples, similar types of laser configurations are also discussed in U.S. Pat. No. 6,208,679.
Accordingly, the output of IBC laser 10 comprises the optical power transmitted by reflective component 17 consisting of wavelength components λi(i=0 to N). The transmitted optical power may be coupled into, for example, optical fiber 18.